Lung cancer accounts for the majority of cancer mortality. Lung squamous cell carcinoma (SCC) accounts for 30% of lung cancer cases, thus the need for further knowledge about prevention and treatment is crucial. Unlike other major cancers, preventive agents and screening guidelines have not been established for lung cancer. The fact that calcitriol, the active metabolite of vitamin D3, has the ability to induce cell cycle arrest, apoptosis and differentiation without toxicity, makes calcitriol an attractive potential agent for chemoprevention of lung cancer. In addition, vitamin D deficiency is associated strongly with the increased risk and poor prognosis of lung cancer. This application falls under the mission of the National Center for Complementary and Alternative Medicine (NCCAM), which fosters research that explores complementary and alternative healing practices in the context of rigorous science. This application addresses their mission by increasing the understanding of the molecular mechanisms of vitamin D a dietary supplement, in efforts to reduce cancer burden thus enhancing the quality of life. We are proposing to investigate the effects of calcitriol in cell lines, clinical samples and an animal model of lung SCC. We hypothesize that treatment of calcitriol will inhibit or slow the growth of the lung squamous cell carcinoma in addition we hope to demonstrate that vitamin D deficiency may enhance disease in vivo. (SA1) To investigate the potential preventive effects of calcitriol in vitro experiments will be carried out in lung SCC and non-malignant bronchial cell lines to examine the molecular effect of calcitriol through the examination of the vitamin D receptor (VDR) and genes that it regulated both directly and indirectly. (SA 2) To further understand the effects of calcitriol and vitamin D deficiency on the development and progression of lung SCC, we are using a carcinogen-induced in vivo model. SWR/J mice are treated topically with the carcinogen, N-nitroso-tri-chloroethylurea (NTCU). The development of lung SCC in the NTCU-induced mouse model closely resembles the formation of human lung SCC beginning with lung hyperplasia progressing to microinvasive carcinoma. These studies will examine the effects of calcitriol and a vitamin D deficient diet on disease progression by evaluating molecular and morphological changes. (SA 3) To further address the clinical significance of this work, VDR status and activity will be measured in bronchial brush samples from an ongoing clinical trial in which trail participants receive 45 mcg weekly to prevent or slow the progression of lung SCC. The overall goal of the project is to determine the preventive effects of vitamin D on lung SCC.